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Trait–environment relationships differ between mixed‐species flocking and non‐flocking bird assemblages
Ecology ( IF 4.8 ) Pub Date : 2020-07-23 , DOI: 10.1002/ecy.3124 Qiang Zhang 1 , Marcel Holyoak 2 , Eben Goodale 3 , Zhifa Liu 4 , Yong Shen 1 , Jiajia Liu 5 , Min Zhang 1 , Anqiang Dong 6 , Fasheng Zou 1
Ecology ( IF 4.8 ) Pub Date : 2020-07-23 , DOI: 10.1002/ecy.3124 Qiang Zhang 1 , Marcel Holyoak 2 , Eben Goodale 3 , Zhifa Liu 4 , Yong Shen 1 , Jiajia Liu 5 , Min Zhang 1 , Anqiang Dong 6 , Fasheng Zou 1
Affiliation
Hypotheses about the mechanisms of community assembly suggest that biotic and abiotic filters constrain species establishment through selection on their functional traits. It is unclear how differences in traits influence the niche dimensions of closely-related bird species when they co-exist in spatiotemporally heterogeneous environments. Further, it is necessary to take into account their participation in mixed-species flocks, social systems that can include both competition and facilitation. For six years, we conducted counts of forest bird species, and took measurements of environmental variables along an elevational gradient in the Nanling Mountains, China. To disentangle different deterministic and historical/stochastic processes between flocking and non-flocking bird assemblages, we first compared phylogenetic and functional structure, and community-weighted mean trait values (CWM). We further assessed elevational variations in trait-environment relationships using a combination of RLQ and fourth-corner analyses. We found that the flocking and non-flocking bird assemblages were structured by environmental gradients in contrasting ways. The non-flocking assemblage showed a strong change from over-dispersed to clustered community structure with increasing elevations, consistent with the strong selective pressures of a harsh environment (i.e. environmental filtering). The non-flocking assemblage also displayed significant trait-environment relationships in bivariate correlations and multivariate ordination space, including specific morphological and foraging traits that are linked to vegetation characteristics (e.g. short trees at high elevations). By contrast, flocking birds were more resilient to habitat change with elevation, with relatively consistent community membership and showed fewer trait-environment associations. CWM of traits that are known to be associated with species' propensity to join mixed-species flocks, including small body size and broad habitat specificity, were linked to the flocking assemblage consistently across the elevational gradient. Collectively, our trait-based analyses provide strong evidence that trait-environment relationships differ between flocking and non-flocking bird assemblages. Besides serving as bellwethers of changing environments, emergent properties of flock systems may increase the resilience of animal communities undergoing environmental change. Mixed-species flocks present an ideal model with which to explore co-occurrence of closely-related species, because habitat filtering may be buffered, and the patterns observed are therefore the outcomes of species interactions including both competition and facilitation.
更新日期：2020-07-23
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